Flavanthrone is the common name for Pigment Yellow 24 (CI 70600). Several processes are known for the production of flavanthrone including (1) treatment of 2-amino-anthraquinone with antimony pentachloride or titanium tetrachloride in nitrobenzene and (2) the Ullmann reaction on acylated 1-chloro-2-amino-anthraquinone followed by alkaline treatment. The crude flavanthrone produced by these known processes is conditioned by acid pasting, i.e., treatment with sulfuric acid and dilution with water. This results in a flavanthrone pigment in a fine state of subdivision suitable for pigment use.
Flavanthrone has a characteristic X-ray pattern exhibiting prominent peaks at about 7.34, 7.00, 3.72, 3.67, 3.52, 3.39 and 3.31 dA. "Prominent peaks" as used herein is intended to denote an intensity of 20 or more based on an intensity scale in which the highest peak is 100.
While useful for many purposes as a yellow pigment, known commercial flavanthrones have not been totally acceptable in the coloration of certain plastics and surface coatings due to the fact that they exhibit opaqueness, i.e., are not sufficiently transparent to produce the desired coloring effect.